staging: sm750fb: Replace kzalloc with devm_kzalloc

Devm_ functions allocate memory that is released when a driver
detaches.
Replace kzalloc with devm_kzalloc and remove corresponding
kfrees from probe and remove functions of a pci_dev.

Also, an unnecessary label has been removed by replacing it
with a direct return statement.

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>