qemu_firmware: Drop 'nvram' local variable

qemu_firmware: Drop 'nvram' local variable

We access the NVRAM information via the 'loader' local variable
throughout the file, and this is the only spot where the 'nvram'
local variable exists. It makes things inconsistent and opens up
the possibility of the values for 'loader' and 'nvram' going out
of sync, especially after a future commit will introduce the
need to set the former. Just get rid of the additional variable.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>