target/mips: fix emulation of nanoMIPS BPOSGE32 instruction

Per the "MIPS® Architecture Extension: nanoMIPS32 DSP Technical
Reference Manual — Revision 0.04" p. 88 "BPOSGE32C", offset argument (imm)
should be left-shifted first.
This change was tested against test_dsp_r1_bposge32.c DSP test.

Reported-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>
Signed-off-by: Filip Vidojevic <filip.vidojevic@syrmia.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <VI1PR0302MB34869449EE56F226FC3C21129C309@VI1PR0302MB3486.eurprd03.prod.outlook.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

target/mips/tcg/translate.c

@@ -21137,7 +21137,7 @@ static int decode_nanomips_32_48_opc(CPUMIPSState *env, DisasContext *ctx)
                                       extract32(ctx->opcode, 0, 1) << 13;
 
                         gen_compute_branch_nm(ctx, OPC_BPOSGE32, 4, -1, -2,
-                                              imm);
+                                              imm << 1);
                     }
                     break;
                 default: