sflash: prevent priority inheritance
sflash: prevent priority inheritance

This patch helps you to prevent priority inheritance while accessing
serial flash.

Change-Id: I38fb00a4e7e9eec819fbd7cfaf053824d1c5143b
Signed-off-by: Byoungtae Cho <d399e7ab5fdc23c09a148b7028e772c5bd5c24c5@samsung.com>

JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT