fota: Fix wrongly written "boot mode" to "upgrade type"

fota: Fix wrongly written "boot mode" to "upgrade type"

The log message for the failure of calling
hal_device_board_get_upgrade_type() function should be about upgrade
type but "boot mode" is used. It should be fixed.

Comparing two string with strncmp, a string variable "upgrade_type" and
constant string "online", compare length should be provided as "sizeof(
upgrade_type)" but "sizeof(boot_mode)" is used.
Their buffer size(boot_mode and upgrade_type) are same so it was not
making any errors so far but it should be fixed.

Change-Id: I580d04d982b943325643aae885bf5c91dae8c0c5
Signed-off-by: SangYoun Kwak <sy.kwak@samsung.com>