Fixes build error with -Werror:
shm/shmfs.c: In function 'shmfs_read':
shm/shmfs.c:122:33: error: pointer of type 'void *' used in arithmetic [-Werror=pointer-arith]
122 | memcpy(buffer, sho->paddr + startpos, nread);
| ^
shm/shmfs.c: In function 'shmfs_write':
shm/shmfs.c:166:25: error: pointer of type 'void *' used in arithmetic [-Werror=pointer-arith]
166 | memcpy(sho->paddr + startpos, buffer, nwritten);
| ^
cc1: all warnings being treated as errors
a37d094f31