target/m68k: fix FPSR quotient byte for fmod instruction

target/m68k: fix FPSR quotient byte for fmod instruction

The FPSR quotient byte should be set to the value of the quotient and not the
result. Switch from using floatx80_mod() to floatx80_modrem() which returns
the quotient as a uint64_t which can be used for the quotient byte.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230114232959.118224-4-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>