vdpa: Follow kdoc comment style

vdpa: Follow kdoc comment style

Follow comment style mentioned in the Writing kernel-doc document [1].

Following warnings are fixed.

$ scripts/kernel-doc -v -none drivers/vdpa/vdpa.c
drivers/vdpa/vdpa.c:67: info: Scanning doc for __vdpa_alloc_device
drivers/vdpa/vdpa.c:84: warning: No description found for return value of '__vdpa_alloc_device'
drivers/vdpa/vdpa.c:153: info: Scanning doc for _vdpa_register_device
drivers/vdpa/vdpa.c:163: warning: No description found for return value of '_vdpa_register_device'
drivers/vdpa/vdpa.c:172: info: Scanning doc for vdpa_register_device
drivers/vdpa/vdpa.c:180: warning: No description found for return value of 'vdpa_register_device'
drivers/vdpa/vdpa.c:191: info: Scanning doc for _vdpa_unregister_device
drivers/vdpa/vdpa.c:205: info: Scanning doc for vdpa_unregister_device
drivers/vdpa/vdpa.c:217: info: Scanning doc for __vdpa_register_driver
drivers/vdpa/vdpa.c:224: warning: No description found for return value of '__vdpa_register_driver'
drivers/vdpa/vdpa.c:233: info: Scanning doc for vdpa_unregister_driver
drivers/vdpa/vdpa.c:243: info: Scanning doc for vdpa_mgmtdev_register
drivers/vdpa/vdpa.c:250: warning: No description found for return value of 'vdpa_mgmtdev_register'

After the fix:

scripts/kernel-doc -v -none drivers/vdpa/vdpa.c
drivers/vdpa/vdpa.c:67: info: Scanning doc for __vdpa_alloc_device
drivers/vdpa/vdpa.c:153: info: Scanning doc for _vdpa_register_device
drivers/vdpa/vdpa.c:172: info: Scanning doc for vdpa_register_device
drivers/vdpa/vdpa.c:191: info: Scanning doc for _vdpa_unregister_device
drivers/vdpa/vdpa.c:205: info: Scanning doc for vdpa_unregister_device
drivers/vdpa/vdpa.c:217: info: Scanning doc for __vdpa_register_driver
drivers/vdpa/vdpa.c:233: info: Scanning doc for vdpa_unregister_driver
drivers/vdpa/vdpa.c:243: info: Scanning doc for vdpa_mgmtdev_register

[1] https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html

Signed-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210406170457.98481-3-parav@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>