msm_rng: Change long to u32 type for buffers reading from RNG HW

Changing the type from long to u32 of the buffer that is used to
read data from the RNG hardware to reflect the size of the HW
register

Change-Id: I54e8eeae40a66c8033637044e627023150d6c411
Acked-by: Baranidharan Muthukumaran <bmuthuku@qti.qualcomm.com>
Signed-off-by: Dinesh K Garg <dineshg@codeaurora.org>