solib-spu: Add gdb_byte* cast

solib-spu: Add gdb_byte* cast

Fixes this error:

/home/simark/src/binutils-gdb/gdb/solib-spu.c: In function ‘file_ptr spu_bfd_iovec_pread(bfd*, void*, void*, file_ptr, file_ptr)’:
/home/simark/src/binutils-gdb/gdb/solib-spu.c:299:55: error: invalid conversion from ‘void*’ to ‘gdb_byte* {aka unsigned char*}’ [-fpermissive]
   ret = target_read_memory (addr + offset, buf, nbytes);
                                                       ^
In file included from /home/simark/src/binutils-gdb/gdb/target.h:65:0,
                 from /home/simark/src/binutils-gdb/gdb/exec.h:23,
                 from /home/simark/src/binutils-gdb/gdb/gdbcore.h:29,
                 from /home/simark/src/binutils-gdb/gdb/solib-spu.c:23:
/home/simark/src/binutils-gdb/gdb/target/target.h:35:12: note:   initializing argument 2 of ‘int target_read_memory(CORE_ADDR, gdb_byte*, ssize_t)’
 extern int target_read_memory (CORE_ADDR memaddr, gdb_byte *myaddr,

gdb/ChangeLog:

	* solib-spu.c (spu_bfd_iovec_pread): Add (gdb_byte *) cast.