sh: fix READ/WRITE redefinition warnings

kernel.h defines READ and WRITE, so rename the SH math-emu macros
to MREAD and MWRITE.

Fixes these warnings:

.../arch/sh/math-emu/math.c:54: warning: "WRITE" redefined
   54 | #define WRITE(d,a) ({if(put_user(d, (typeof (d) __user *)a)) return -EFAULT;})
In file included from ../arch/sh/math-emu/math.c:10:
.../include/linux/kernel.h:37: note: this is the location of the previous definition
   37 | #define WRITE   1
.../arch/sh/math-emu/math.c:55: warning: "READ" redefined
   55 | #define READ(d,a) ({if(get_user(d, (typeof (d) __user *)a)) return -EFAULT;})
In file included from ../arch/sh/math-emu/math.c:10:
.../include/linux/kernel.h:36: note: this is the location of the previous definition
   36 | #define READ   0

Fixes: 4b565680 ("sh: math-emu support")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Takashi YOSHII <takasi-y@ops.dti.ne.jp>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Rich Felker <dalias@libc.org>