vfb: Fix parsing of command line args

The bpp and memsize values need to be extracted based on the command
line arguments. Use strncmp to compare only the string part to extract
the values.

Change-Id: I51ec868d0f636cb755318f935534eb23d98e3695
Signed-off-by: Channagoud Kadabi <ckadabi@codeaurora.org>