target/sparc: Fix gdbstub incorrectly handling registers f32-f62

target/sparc: Fix gdbstub incorrectly handling registers f32-f62

The gdbstub implementation for the Sparc architecture would
incorrectly calculate the the floating point register offset.
This resulted in, for example, registers f32 and f34 to point to
the same value.

The issue was caused by the confusion between even register numbers
and even register indexes. For example, the register index of f32 is 64
and f34 is 65.

Cc: qemu-stable@nongnu.org
Fixes: 30038fd81808 ("target-sparc: Change fpr representation to doubles.")
Signed-off-by: Mikael Szreder <git@miszr.win>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20250214070343.11501-1-git@miszr.win>
(cherry picked from commit 7a74e468089a58756b438d31a2a9a97f183780d7)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>