config/tc-avr.c (md_section_align): Append UL for -1 to avoid the latest gcc's warning

config/tc-avr.c (md_section_align): Append UL for -1 to avoid the latest gcc's warning

The related warning is:

  gcc -DHAVE_CONFIG_H -I. -I../../binutils-gdb/gas  -I. -I../../binutils-gdb/gas -I../bfd -I../../binutils-gdb/gas/config -I../../binutils-gdb/gas/../include -I../../binutils-gdb/gas/.. -I../../binutils-gdb/gas/../bfd -DLOCALEDIR="\"/upstream/release-avr32/share/locale\""  -W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wshadow -Werror -I../../binutils-gdb/gas/../zlib -g -O2 -MT tc-avr.o -MD -MP -MF .deps/tc-avr.Tpo -c -o tc-avr.o `test -f 'config/tc-avr.c' || echo '../../binutils-gdb/gas/'`config/tc-avr.c
../../binutils-gdb/gas/config/tc-avr.c: In function ‘md_section_align’:
../../binutils-gdb/gas/config/tc-avr.c:1233:43: error: left shift of negative value [-Werror=shift-negative-value]
     return ((addr + (1 << align) - 1) & (-1 << align));
                                             ^

2015-09-05  Chen Gang  <gang.chen.5i5j@gmail.com>

	* config/tc-avr.c (md_section_align): Append UL for -1 to avoid
	the latest gcc's warning.