In read_insn_microblaze() we assemble 4 bytes into an 'unsigned
long'.  If 'unsigned long' is 64 bits and the high byte has its top
bit set, then C's implicit conversion from 'unsigned char' to 'int'
for the shift will result in an unintended sign extension which sets
the top 32 bits in 'inst'.  Add casts to prevent this.  (Spotted by
Coverity, CID 10054016.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 1488556233-31246-5-git-send-email-peter.maydell@linaro.org