media: camss: vfe: Rework vfe_hw_version_read() function definition

Expose the VFE version by returning the value read from the HW_VERSION
register.

Secondly, change the name of this function to conform with the CSID
equivalent.

Signed-off-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>