usb: gadget: f_fs: Prevent panic due to failure of huge size buffer allocation

usb: gadget: f_fs: Prevent panic due to failure of huge size buffer allocation

The f_fs daemons usually use large size buffer for increasing transfer
performance, but it can cause memory allocation failure in case of
that buddy space is fragmented. Since this, instead of just returning
error in this case, give the chance to retry to allocate memory with
a half length in order to prevent daemon crash due to failure of
buffer allocation.

Signed-off-by: Dongwoo Lee <dwoo08.lee@samsung.com>
[hoegeun.kwon: rebased and resolved conflicts]
Signed-off-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Change-Id: Ief5f8256b37b38de14bb333e53c4c4688867d4f6