msm: mhi_dev: Changing the GFP flag in alloc_skb()

GFP_ATOMIC flag is typically used in memory allocations inside
interrupt handlers or with spin locks. It is of high priority but it
does not allow the caller to reclaim the memory allocation request.
This may lead to memory allocation failures in low memory situations.

Since alloc_skb() is not called from interrupt handler or in spin lock
context, changing the GFP flag from GFP_ATOMIC to GFP_KERNEL.

Change-Id: I6c3a2b5b4674965cf1d4860e9072fa46cd4adddb
Signed-off-by: Sai Chaitanya Kaveti <quic_skaveti@quicinc.com>