udmabuf: fix a buf size overflow issue during udmabuf creation

[ Upstream commit 021ba7f1babd029e714d13a6bf2571b08af96d0f ]

by casting size_limit_mb to u64  when calculate pglimit.

Signed-off-by: Xiaogang <Chen&lt;Xiaogang.Chen@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250321164126.329638-1-xiaogang.chen@amd.com


Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>