hw/mips_malta: Fix YAMON API print routine

The print routine provided as part of the in-built bootloader had a bug
in that it attempted to use a jump instruction as part of a loop, but
the target has its upper bits zeroed leading to control flow
transferring to 0xb0000814 rather than the intended 0xbfc00814. Fix this
by using a branch instruction instead, which seems more fit for purpose.

A simple way to test this is to build a Linux kernel with EVA enabled &
attempt to boot it in QEMU. It will attempt to print a message
indicating the configuration mismatch but QEMU would previously
incorrectly jump & wind up printing a continuous stream of the letter E.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Leon Alrae <leon.alrae@imgtec.com>
Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
